I am of the opinion that the best teachers for up to mid-B1 are those who have the same native language as you do -- but know the target language very, very well. They can give you the best translations, the best tips and help you understand your errors and get rid of them far better than a teacher who has no idea why you are messing up where you are. 

After around mid-B1, beginning of B2  you should have a native speaker for a teacher, and from mid-B2 upwards it doesn't matter if they speak your language or not, really. Nice if they know some, but not necessary. 

Personally, I hate being forced to speak before I'm ready and I hate having complex grammar info given to me in the target language when I can barely ask where the washroom is. I'm not lazy, when I feel I can handle beginning to speak in the target language, I will. Until then....English, if you don't mind. 

I remember a situation when I didn’t understand a French grammatical point. The teacher tried to explain it in French and it just got worse because I didn’t understand her explanations and the examples she had given. After, what seemed a lifetime and the perplexed expression on her face, she explained it in English. Within twenty seconds, I’d got it.

So, I prefer to be taught in the language I’m learning, but if there is some points I’ll not understand in French, then I’d like those to be explained in English and then I can explain it in French to the teacher. So I prefer a teacher that can speak my language, for those instances.

I'm learning Spanish. I have one teacher who speaks English (very well), and one who doesn't. I think both kinds are very useful, in different ways. Each of them gives me something I don't get from the other.

As an intermediate speaker, I cannot avoid asking myself "do I actually 'know Spanish' yet?" It's a silly question. But I remember, with great pleasure, one time. I was about my twelfth lesson with the non-English-speaking teacher, and I suddenly realized for the first time that she didn't speak English. I was able to say to myself, "Well, if I have been communicating for hours, pretty well, with a person who does not speak English, I guess I can start to say 'I speak a little Spanish!'" Talking to a non-English speaker is "the real thing." There are no crutches, no shortcuts. If I don't know a word, I need to figure out how to ask about it using words I do know. If she says something I don't understand, I need to ask her to explain it in Spanish.

There are no shortcuts! I can't say "¿como se dice 'lightning' en español?" I have to say (in Spanish) "What is the name for the bright flashes of light, made by electricity, in a storm?"

With the English-speaking teacher, we can discuss the language itself and she can help me understand grammar and shades of meaning by pointing out similarities and differences with English. And, of course, when we really get stuck, I can always ask in English, and she can explain or translate in English.

If I had to choose, I would say there are plenty of resources--in textbooks and online--that give me Spanish examples with English explanations. The experience of really being forced to use the target language is something you can only get with a teacher who does not speak your language.